lecture 2 - minerals (chapter 3)

8/13/2019 Lecture 2 - Minerals (Chapter 3)

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Minerals, rocks & soils

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Every civil engineering structure builton this Earth must interact with

either rocks or soils

All rocks & soils are composed of aheterogeneous assortment of

(related) minerals

These minerals are partially

responsible for the physical andchemical properties of these rocks &

soils


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The nature of minerals

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Minerals are:

1. naturally occurring,

2. inorganic,

3. solid,

4. ordered with internal

molecular structure,

5. characteristic

chemical composition.


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Internal structure

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Atomic structure

central region called the nucleus:

consists of protons (+ charge)and neutrons (no charge)

atomic number: # of protons

atomic weight: # or protons &

neutrons

electrons :

particles (charge) that

surround the nucleus

located in discrete energy

levels called shells

valence elections are those

that are outermost in the shell

and lead to oxidation state


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Ionic bonds

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Anion: an atomthat picks up an

extra electron and

becomes

negatively charged

Cation: an atomthat looses an

electron and

becomes positivelycharged

Ionic compounds:orderly array of

oppositely chargedions assembled in

a definite ratio that

provides overall

electrical neutrality


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Covalent bonds

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Covalent bondsinvolve sharing

electrons betweenatoms

Silica is the basic building

block of the vast majority of rocks

and soils


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Crystals

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Polymorph: someelements can join together

in more than one geometric

arrangement

chemical composition

stays the same

physical properties

differ

diamond & graphite


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Habit (shape)

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External expression of the orderly internal arrangement ofatoms

Crystal growth is often interrupted because of competition for

space within the host rock, and the rate at which lava (liquid)cools to the solid rock containing the mineral


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Cleavage

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Cleavage plane: tendency formineral to break along planes of

weak bonding within the internalcrystal structure

Produces flat shiny surfaces

Surfaces are characterized bygeometric shapes

Number of planes

Angles between adjacent planes


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Cleavage

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Fracture

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Crystals that are composed of atomsthat are evenly spaced and equally

attracted to adjacent atoms in all

directions fracture because theycannot form cleavage planes

Concoidal fracture: smooth curvedsurfaces resembling broken glass

Quartz sometimes displays thisfeature


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Colour & Streak

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The colour of a mineralspecimen is an obvious, but

not a diagnostic feature

The streak of a mineral is itscolour in powder form, and its

colour does not usually vary

from sample to sample


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Lustre

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Lustre is the appearance or quality of light reflected from the surface ofthe mineral crystal

metallic lustre nonmetallic lustre (e.g.glassy, pearly, silky,resinous, earthy)


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Other properties

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lecture 2 - minerals (chapter 3)

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